1. Field of the Invention
The present invention relates to circuitry for controlling the display of an on-screen display (OSD) window within a video display, and in particular, to fade control circuitry for providing fade in and fade out control over an OSD window.
2. Description of the Related Art
Referring to FIG. 1, as video display devices have increased in complexity and sophistication, particularly computer monitors, it is increasingly common for the display 10 in which a video image 12 is displayed to also include an OSD region, or window, 20 in which OSD information is displayed, such as one or more lines of OSD characters. One feature which has become increasingly popular is fading of the OSD window 20, whereby the vertical 20v and 20h dimensions of the OSD window 20 are selectively increased (fade in) or decreased (fade out) when opening or closing, respectively, the OSD window 20. This is typically done by initiating the opening and terminating the closing at the top left corner 20c of the OSD window 20. Between its fully closed and fully opened states, the OSD window will have a number of intermediate sizes as indicated by the dashed lines 20vi, 20hi representing the intermediate vertical and horizontal dimensions of such intermediate windows.
Opening or closing of the OSD window 20 is normally timed to be less than one second, e.g., approximately 0.5 second. The time intervals for the opening or closing of the window 20 in the horizontal and vertical directions can be fixed, or variable dependent upon the size of the window 20. While fixing such time interval would make the implementation of the control circuitry for doing this a simpler task, the size and shapes of OSD windows 20 are often variable. Accordingly, using fixed time intervals would cause the opening and closing times for a small OSD window to be faster than for a larger window. Hence, for a small OSD window, the resulting fade in and fade out effects would appear minimal.